The present invention relates generally to graphical display of spectral data, and more specifically to user interface enhancements that facilitate the examination and manipulation of such data.
Spectral analysis is often used to determine the qualitative or quantitative composition of a sample. Typical spectral data consist of the absorbance of the sample or specimen at different wavelengths or frequencies of light. Absorbance data are typically plotted against inverse wavelength (a measure of frequency referred to as wavenumber), with the resulting graph being referred to as a spectrum. Also note that while the discussion of typical usage is appropriately in terms of wavenumber vs. absorbance, many of the same manipulations are applicable to a number of other y units (such as %Transmittance, reflectance, Volts) and x units (such as optical retardation of an interferogram, microns, electron Volts).
In order to interpret spectrum, raw data collected from a sample may require additional manipulations:
(1) Specific sampling techniques affect raw spectral data in known, predictable ways; manipulations can convert the data into a sampling-independent standard form. PA1 (2) Sample preparation and sampling techniques may introduce artifacts, and data manipulations may be applied to correct these. PA1 (3) Many samples are mixtures, and manipulations are required to determine the spectrum and concentrations of the individual compounds present.
In order to eliminate known artifacts and eliminate known components from a sample compound, the data points of the sample spectrum are commonly modified. In one method, each spectral data point in the sample spectrum S, is modified by a corresponding data point representing a known sample compound, in the form of a reference spectrum R. The resulting modified spectrum Z, is related to S and R by equation (1), where a and b are scalar values. EQU Z=S-(a*R)+b (1)
Typically, the user inputs a value for "a" and "b" and the processor calculates the modified spectrum Z. After observing the results of the modified spectrum Z, the user can again modify the values for "a" and "b" and review the new spectrum Z. This process is repeated until the user is satisfied with the appearance of the modified spectrum Z. The same modification process of a sample spectrum is used in determining the composition of the sample or is used in adjusting the baseline offset of the spectrum.
The user often magnifies portions of the sample spectrum to concentrate his analysis. Current systems allow the user the ability to increase or decrease the amount of the spectrum, i.e. the range of wave numbers, that is displayed to the user.